1. Field of the Invention
The present invention relates to an integrated circuit for memorizing and storing information confidentially, including an anti-fraud device. It relates more particularly, but not exclusively, to integrated circuits of the above type known as memory cards.
2. Description of the Prior Art
Memory cards are formed with an integrated electronic circuit including essentially an electrically programmable non volatile memory often having non modifiable confidential data, input/output means for coupling the circuit to a data transfer device and processing means interconnected between the input/output means and the memory. In some applications of the memory cards, it is essential to protect the access to certain zones of the non volatile memory by an access key such as a confidential code associated with certain rights of reading or writing in the specific zones. There exist numerous devices for dissauding defrauders who seek to discover the secret code or the access key to a memory by successive attempts.
Among these devices, the most widely known is doubtless the one which permanently memorizes the key presentation errors and blocks operation of the circuit as soon as the number of errors exceeds a predetermined value. with such devices there is generally associated a logic which prevents the insertion of a correct key from being monitored by observing variations of the supply currents of a circuit. The defrauder cannot therefore be informed of the results of the attempts he has undertaken.
Now, such devices require a relatively large space in the memory for recording the correct attempts which are in fact the most frequent. In the case where the card has relatively simple functions, such complex processing which requires a great deal of space on the component, cannot be justified. There is then hesitation in using such an antifraud device. Moreover, it is required in certain applications, on the contrary, to reinforce the antifraud detection device.